The correct answer is - Ridge.
The new crust in the oceans forms where there's divergent plate boundaries. That means a place where two or more tectonic plates move away from one another, thus living a gap behind them. Through that gap, the enormous temperatures, high pressure, and the magma, from the mantle layer, manage to penetrate towards the ocean floor. As the magma reaches the ocean floor it cools of very quickly and new crust is forming. Because the magma is continuously coming out, an underwater mountains range is forming, known as a mid-ocean ridge, which is actually the place where the youngest crust can be found.
